java - PaintComponent 从未被调用

Question

我已经研究了一天了，我不明白为什么不调用 paintComponent(Graphics g) 方法。我使用第二个构造函数来实例化对象，但仍然没有任何结果。我的室友有一个非常相似的代码并且有效。我做错了什么？

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;

import javax.swing.JPanel;

public class squareImage extends JPanel{

Image picture;
String name;
baharKa outerPanel;    // a panel that I add these sqaures in
String topLabel;

int a = 0;
int b = 0;

public squareImage(baharKa out, String top, String name, Image im){  //This is the first constructor
    this.outerPanel = out;
    this.name = name;
    this.picture  = im;
    this.topLabel = top;
    this.setPreferredSize(new Dimension(80, 60));
    this.setBounds(a, b, getWidth(), getHeight());
    this.setPreferredSize(new Dimension(80,80));
    this.setOpaque(false);
}

public squareImage(baharKa out, String top, String name, Image im, int a, int b){  //This is second contructor
    this(out, top, name, im);
    this.a = a;
    this.b = b;
    this.setBounds(a, b, getWidth(), getHeight());
    out.revalidate();
}

protected void paintComponent(Graphics g) {     //This is never called
    super.paintComponent(g);
    System.out.println ("hi!");
    int i = g.getFontMetrics().stringWidth(name);
    int j = g.getFontMetrics().stringWidth(topLabel);
    g.drawImage(picture, 20, 20, 40, 40, null);
    g.setColor(Color.BLACK);
    g.setFont(new Font("Calibri", Font.PLAIN, 12));
    g.drawString(name, i/2 + 40, 45);
    g.drawString(name, j/2 + 40, 15);
}

}

/////////我在这里使用它///////

protected void showMeTheSquares(){
        try {
            System.out.println("showme");
            wood = new squareImage(baharKaPanel, "0", "Wood", ImageIO.read(new File("images/wood.png")), 200, 75);
            metal = new squareImage(baharKaPanel, "0", "Metal", ImageIO.read(new File("images/metal.png")), 300, 75);
            plastic = new squareImage(baharKaPanel, "0", "Plastic", ImageIO.read(new File("images/plastic.png")), 400, 75);
            screwD = new squareImage(baharKaPanel, "0", "Plastic", ImageIO.read(new File("images/screwdriver.png")), 10, 100);
            hammer = new squareImage(baharKaPanel, "0", "Hammer", ImageIO.read(new File("images/hammer.png")), 10, 180);
            pliers = new squareImage(baharKaPanel,"0", "Pliers", ImageIO.read(new File("images/pliers.png")), 10, 340);
            scissors = new squareImage(baharKaPanel,"0", "Scissors", ImageIO.read(new File("images/scissors.png")), 10, 420);
            brush = new squareImage(baharKaPanel, "0", "Paint Brush", ImageIO.read(new File("images/paintbrush.png")), 10, 260);
            wood.repaint();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        addEverything();

    }

    protected void addEverything(){

        baharKaPanel.add(wood);
        baharKaPanel.add(metal);
        baharKaPanel.add(plastic);
        baharKaPanel.add(screwD);
        baharKaPanel.add(hammer);
        baharKaPanel.add(pliers);
        baharKaPanel.add(scissors);
        baharKaPanel.add(brush);
    }

Answer 1

这和您对空布局的使用将创建一个 0 x 0 大小的组件:

this.setBounds(a, b, getWidth(), getHeight());

如果您此时输入代码并打印出 getWidth() 和 getHeight() 在未渲染的组件中返回的内容，您将发现是 0 或 1。

无论如何，您都不应该使用空布局或设置边界，而应该使用尊重首选尺寸的布局管理器，因为使用空布局会导致 GUI 非常不灵活，虽然它们在一个平台上看起来不错，但在一个平台上看起来很糟糕大多数其他平台或屏幕分辨率，并且很难更新和维护。